Abstract: A method for providing corrected x-ray images of a recording object and a correspondingly configured x-ray system are provided. In the method, a first x-ray image recorded prior to introducing a contrast agent and a second x-ray image of the recording object recorded after introducing the contrast agent are provided. A ring correction for eliminating ring artifacts is applied to the first x-ray image and the second x-ray image in each case. In order to provide corrected x-ray images with an improved image quality, provision is made with the ring correction of the first x-ray image for a ring image, which contains artifact data extracted from the first x-ray image, to be obtained and stored and for the ring correction of the second x-ray image for the ring image obtained with the ring correction of the first x-ray image to be used.

Abstract: A method is for determining a transformation for image registration of a first image relative to a second image. The method includes ascertaining a test series of test elements including a test transformation and a test value, the ascertaining including ascertaining the test transformation based on a sequence of test transformations and/or based on previously ascertained test elements, transforming the first image via the ascertained test transformation, ascertaining a difference image, and ascertaining the test value of the test element based on the difference image such that the test value is a measure for an extension of a frequency distribution of values of pixels of the difference image in a direction of pixel value increase. It further includes determining a minimum test value based on test values encompassed by the test elements and determining the transformation which is the test transformation of a test element including the minimum test value.

Abstract: A method for providing corrected x-ray images of a recording object and a correspondingly configured x-ray system are provided. In the method, a first x-ray image recorded prior to introducing a contrast agent and a second x-ray image of the recording object recorded after introducing the contrast agent are provided. A ring correction for eliminating ring artifacts is applied to the first x-ray image and the second x-ray image in each case. In order to provide corrected x-ray images with an improved image quality, provision is made with the ring correction of the first x-ray image for a ring image, which contains artifact data extracted from the first x-ray image, to be obtained and stored and for the ring correction of the second x-ray image for the ring image obtained with the ring correction of the first x-ray image to be used.

Abstract: A method is for determining a transformation for image registration of a first image relative to a second image. The method includes ascertaining a test series of test elements including a test transformation and a test value, the ascertaining including ascertaining the test transformation based on a sequence of test transformations and/or based on previously ascertained test elements, transforming the first image via the ascertained test transformation, ascertaining a difference image, and ascertaining the test value of the test element based on the difference image such that the test value is a measure for an extension of a frequency distribution of values of pixels of the difference image in a direction of pixel value increase. It further includes determining a minimum test value based on test values encompassed by the test elements and determining the transformation which is the test transformation of a test element including the minimum test value.